Electrical and mechanical properties of antistatic PVC films containing multi-layer graphene

In order to explore practical application of graphene as novel conductive fillers in the filed of composite materials, we prepared anti-static multi-layer graphene (MLG) filled poly(vinyl chloride) (PVC) composite films by using conventional melt-mixing method, and investigated electrical conductivity, tensile behavior, and thermal properties of the MLG/PVC composite films. We found that the presence of MLG can greatly increase electrical conductivity of the MLG/PVC composites, and the surface electrical conductivity of the MLG/PVC composites is less than 3 × 10⁸ Ohm/square when the MLG loading is about 3.5 wt%, meeting anti-static requirement for commercial anti-static PVC films. On the other hand, the MLG/PVC composites exhibited higher tensile modulus and higher glass transition temperature than neat PVC, which is closely associated with crumpled morphology of the MLG and good compatibility between components of the MLG/PVC composites. By virtue of its satisfied anti-static performance and high mechanical properties, the MLG/PVC composites exhibit great potential to be used as high-performance antistatic materials in many fields.     

Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapour deposition

Integration of individual two-dimensional graphene sheets into macroscopic structures is essential for the application of graphene. A series of graphene-based composites and macroscopic structures have been recently fabricated using chemically derived graphene sheets. However, these composites and structures suffer from poor electrical conductivity because of the low quality and/or high inter-sheet junction contact resistance of the chemically derived graphene sheets. Here we report the direct synthesis of three-dimensional foam-like graphene macrostructures, which we call graphene foams (GFs), by template-directed chemical vapour deposition. A GF consists of an interconnected flexible network of graphene as the fast transport channel of charge carriers for high electrical conductivity. Even with a GF loading as low as ～0.5 wt%, GF/poly(dimethyl siloxane) composites show a very high electrical conductivity of ～10 S cm(-1), which is ～6 orders of magnitude higher than chemically derived graphene-based composites. Using this unique network structure and the outstanding electrical and mechanical properties of GFs, as an example, we demonstrate the great potential of GF/poly(dimethyl siloxane) composites for flexible, foldable and stretchable conductors.     

Highly controllable and green reduction of graphene oxide to flexible graphene film with high strength

Graphene film with high strength was fabricated by the assembly of graphene sheets derived from graphene oxide (GO) in an effective and environmentally friendly approach. Highly controllable reduction of GO to chemical converted graphene (CCG) was achieved with sodium citrate as a facile reductant, in which the reduction process was monitored by XRD analysis and UV–vis absorption spectra. Self-assembly of the as-made CCG sheets results in a flexible CCG film. This method may open an avenue to the easy and scalable preparation of graphene film with high strength which has promising potentials in many fields where strong, flexible and electrically conductive films are highly demanded.     

改性石墨烯/聚氯乙烯复合材料的制备及性能

采用不同含量的硅烷偶联剂γ-甲基丙烯酰氧基丙基三甲氧基硅烷（KH570）对石墨烯（GE）进行改性,将改性GE（KH-GE）与聚氯乙烯（PVC）进行熔融混炼制备KH-GE/PVC复合材料。通过FTIR、Raman、XRD、TEM和SEM表征改性前后GE结构变化,并考察了KH-GE/PVC复合材料的力学性能、导电性能及稳定性能。结果表明,GE∶KH570质量比为1∶2时,KH-GE的层间距较大,改善了GE的团聚,使GE在PVC基体中的分散得到了改善。随着KH-GE含量的增加,KH-GE/PVC复合材料的力学性能显著提高,当KH-GE质量分数为1.5wt%时,KH-GE/PVC复合材料的拉伸强度和断裂伸长率分别为23.98 MPa和226.78%,比未添加KH-GE的PVC复合材料分别提高了51.1%和65.73%;相对于纯PVC,当KH-GE质量分数为1.5wt%时,对应的50%热失重（T_50%）及90%热失重（T_90%）分别从289.81℃和486.01℃提高到298.51℃和596.53℃,提高了KH-GE/PVC复合材料的热稳定性,导电性也显著提高。     

Thermal and electrical conductivity of Al(OH)<Subscript>3</Subscript> covered graphene oxide nanosheet/epoxy composites

Al(OH)₃ functionalized graphene composites (Al–GO) were prepared using a simple sol–gel method. In this protocol, graphene oxide (GO) was prepared according to the Hummers method and functionalized to enhance its reactivity with aluminum isopropoxide by a LiAlH₄ treatment. The functionalized graphene sheets were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. These analyses confirmed that GO had been fabricated and the Al(OH)₃ layer could have a homogeneous distribution with large and dense coverage onto GO sheets. In addition, the thermal and electrical conductivity of the epoxy composites with GO and Al–GO fillers were measured. The thermal conductivities of the composites with graphene-based fillers were enhanced by the addition of fillers. In particular, the thermal conductivity of GO/epoxy composite containing 3 wt% was approximately two times higher than that of pure epoxy resin. In addition, the electrical conductivity of Al–GO embedded composites degenerated compared to GO composites.     

Electrical and mechanical properties of PMMA/reduced graphene oxide nanocomposites prepared via in situ polymerization

We report the effect of filler incorporation techniques on the electrical and mechanical properties of reduced graphene oxide (RGO)-filled poly(methyl methacrylate) (PMMA) nanocomposites. Composites were prepared by three different techniques, viz. in situ polymerisation of MMA monomer in presence of RGO, bulk polymerization of MMA in presence of PMMA beads/RGO and by in situ polymerization of MMA in presence of RGO followed by sheet casting. In particular, the effect of incorporation of varying amounts (i.e. ranging from 0.1 to 2 % w/w) of RGO on the electrical, thermal, morphological and mechanical properties of PMMA was investigated. The electrical conductivity was found to be critically dependent on the amount of RGO as well as on the method of its incorporation. The electrical conductivity of 2 wt% RGO-loaded PMMA composite was increased by factor of 10⁷, when composites were prepared by in situ polymerization of MMA in the presence of RGO and PMMA beads, whereas, 10⁸ times increase in conductivity was observed at the same RGO content when composites were prepared by casting method. FTIR and Raman spectra suggested the presence of chemical interactions between RGO and PMMA matrix, whereas XRD patterns, SEM and HRTEM studies show that among three methods, the sheet-casting method gives better exfoliation and dispersion of RGO sheets within PMMA matrix. The superior thermal, mechanical and electrical properties of composites prepared by sheet-casting method provided a facile and logical route towards ultimate target of utilizing maximum fraction of intrinsic properties of graphene sheets.     

石墨烯含量对铜基石墨烯复合材料力学和电学性能的影响

为改进铜基复合材料的力学和电学性能,向铜基体分别加入0.2%、0.3%、0.4%(质量分数)的石墨烯,充分混合后,采用放电等离子烧结技术(SPS)制备了石墨烯/铜(G/Cu)复合材料。通过扫描电镜(SEM)、拉曼(Raman)光谱和XRD等表征了复合材料微观结构,测试了其硬度、屈服强度、抗压强度和导电率等性能,以确定石墨烯在铜基体中的合适掺杂量。结果表明:随着石墨烯含量的降低,其力电性能显著提高。当石墨烯质量分数为0.2%时,G/Cu复合材料的综合性能(力学及电学性能)达到最好匹配,实现了铜基材料的高强度、高导电性:其抗压强度和屈服强度分别为557.23 MPa和256 MPa,相对于用SPS方法制备的纯铜分别提高了59.21%和70.7%;电导率为52.3 MS/m,其IACS高达91.8%。     

石墨烯/纳米银复合材料的制备、微结构及其导电性能

将不同比例的氧化石墨烯(GO)和硝酸银混合,采用水合肼一步还原制备石墨烯/纳米银(RGO/Ag)复合材料。采用UV-vis、XRD、FTIR和SEM对RGO/Ag复合材料结构组成进行表征分析,并结合热流量和结构变化研究其构成和热处理工艺对导电性的影响。结果表明:Ag基本以类似球形与石墨烯(RGO)复合;RGO/Ag复合材料的导电性与其构成有很大关系,只有当GO加入量小于50wt%时,Ag含量的提高和热处理工艺的优化可以明显改善复合材料的导电性,其中,GO加入量为16wt%的RGO/Ag片方阻值可达到8mΩ/□;当GO加入量高于50wt%时,复合材料导电性与RGO接近,受Ag含量的提高和热处理工艺优化的影响较小。     

Elastic properties of chemically derived single graphene sheets

The elastic modulus of freely suspended graphene monolayers, obtained via chemical reduction of graphene oxide, was determined through tip-induced deformation experiments. Despite their defect content, the single sheets exhibit an extraordinary stiffness ( E = 0.25 TPa) approaching that of pristine graphene, as well as a high flexibility which enables them to bend easily in their elastic regime. Built-in tensions are found to be significantly lower compared to mechanically exfoliated graphene. The high resilience of the sheets is demonstrated by their unaltered electrical conductivity after multiple deformations. The electrical conductivity of the sheets scales inversely with the elastic modulus, pointing toward a 2-fold role of the oxygen bridges, that is, to impart a bond reinforcement while at the same time impeding the charge transport.     

Intumescent flame retardant polyurethane/reduced graphene oxide composites with improved mechanical, thermal, and barrier properties

Intumescent flame retardant polyurethane (IFRPU) composites were prepared in the presence of reduced graphene oxide (rGO) as synergism, melamine, and microencapsulated ammonium polyphosphate. The composites were examined in terms of thermal stability (both under nitrogen and air), electrical conductivity, gas barrier, flammability, mechanical, and rheological properties. Wide-angle X-ray scattering and scanning electron microscopy indicated that rGO are well-dispersed and exfoliated in the IFRPU composites. The limiting oxygen index values increased from 22.0 to 34.0 with the addition of 18 wt% IFR along with 2 wt% rGO. Moreover, the incorporation of rGO into IFRPU composites exhibited excellent antidripping properties as well as UL-94 V0 rating. The thermal stability of the composites enhanced. This was attributed to high surface area and good dispersion of rGO sheets induced by strong interactions between PU and rGO. The oxygen permeability, electrical, and viscoelasticity measurements, respectively, demonstrated that rGO lead to much more reduction in the gas permeability (by ~90 %), high electrical conductivity, and higher storage modulus of IFRPU composites. The tensile strength, modulus, and shore A remarkably improved by the incorporation of 2.0 wt% of rGO as well.     

Improving the thermal and mechanical properties of silicone polymer by incorporating functionalized graphene oxide

Functionalized graphene oxide (FGO) was produced by reacting graphene oxide nanosheets with vinyl trimethoxy silane (VTMS). The results confirmed the attachment of VTMS molecules to the surface of GO sheets by Si–O–C bonding. The introduction of VTMS molecules led to an excellent dispersibility in tetrahydrofuran and to the complete exfoliation of FGO with a thickness of about 1.19 nm. Meanwhile, FGO/silicone polymer composites were prepared by solution blending method. The incorporation of 0.5 wt% of FGO in silicone polymer improved remarkably the thermal stability, tensile strength, and thermal conductivity of the silicone polymer composite, due to the homogeneous dispersion of FGO in the composites as well as to the strong interfacial adhesion with silicone polymer matrix. Tensile strength and thermal conductivity of the FGO/silicone polymer composite were increased by 95.6 and 78.3 %, respectively, with the addition of 0.5 wt% FGO. The 5 % weight loss temperature of the composite at 0.5 wt% FGO loading was detected 26.1 °C higher than that of silicone polymer.     

Functional composite materials based on chemically converted graphene

Graphene, a one-atom layer of graphite, possesses a unique two-dimensional structure and excellent mechanical, thermal, and electrical properties. Thus, it has been regarded as an important component for making various functional composite materials. Graphene can be prepared through physical, chemical and electrochemical approaches. Among them, chemical methods were tested to be effective for producing chemically converted graphene (CCG) from various precursors (such as graphite, carbon nanotubes, and polymers) in large scale and at low costs. Therefore, CCG is more suitable for synthesizing high-performance graphene based composites. In this progress report, we review the recent advancements in the studies of the composites of CCG and small molecules, polymers, inorganic nanoparticles or other carbon nanomaterials. The methodology for preparing CCG and its composites has been summarized. The applications of CCG-based functional composite materials are also discussed.     

Alkylated graphene nanosheet composites with polyaniline nanofibers

We demonstrate a simple method to prepare alkylated graphene/polyaniline composites (a-GR/PANI) using solution mixing of exfoliated alkyl Iodododecane treated graphene oxide sheets with polyaniline nanofiber; polyaniline nanofibers (PANI) prepared by using rapid mixing polymerization significantly improve the processibility of polyaniline and its performance in many conventional applications. Also, polyaniline nanofibers exhibit excellent water dispersibility due to their uniform nanofiber morphology. Morphological study using SEM and TEM analysis showed that the fibrous PANI in the composites a-GR/PANI mainly adsorbed onto the surface or intercalated between the graphene sheets, due especially to the good interfacial interaction between the alkylated gaphene and the polyaniline nanofibers. The existence of polyaniline nanofibers on the surface of the garphene and the alkylated graphene sheets was confirmed by using FT-IR, FT-Raman and X-ray diffraction analysis. Due to the good interfacial interaction between the alkylated graphene and the polyanilines nanofibers, the composite (a-GR/PANI) exhibited excellent dispersion stability in DMF compared to the same composite (GR/PANI) without alkylation. The electrical conductivity of the (GR/PANI) composite was 9% higher than that of pure PANI and the same weight percent for the composite after alkylation was 13% higher than that of pure PANI nanofibers.     

Diazonium functionalization of graphene nanosheets and impact response of aniline modified graphene/bismaleimide nanocomposites

For developing high performance of graphene-based nanocomposites, dispersibility of graphene sheets in matrices and interfacial interaction are challenging due to the strong tendency of agglomeration and surface inertia of graphene. Here we report an efficient way to functionalize graphene nanosheets with aniline groups on their surfaces, to attain the functionalized graphene nanosheets (FGS) by diazonium treatment following reduction of graphene oxide with hydrazine hydrate. Two kinds of nanocomposites based on diallyl bisphenol A modified bismaleimide (BMI-BA) resin which was filled with functionalized graphene and reduced graphene oxide nanosheets were prepared, and the FGS were linked with BMI resin by chemical bonds. The FGS/BMI-BA composite at a loading of 0.3 wt% revealed a 39% increase in impact strength and a slightly improvement in flexural strength, and the resulting composite remains stable at high temperature. This work provides more possibilities for incorporation of graphene into polymer matrices and an efficient method to toughening the BMI resin.     

Synthesis and characterization of electrochemically-reduced graphene

Graphene has superior electrical conductivity than graphite and other allotropes of carbon because of its high surface area and chemical tolerance. Electrochemically processed graphene sheets were obtained through the reduction of graphene oxide from hydrazine hydrate. The prepared samples were heated to different temperatures such as 673 and 873 K. X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), transmission electron microscopy (TEM), Raman spectra and conductivity measurements were made for as-prepared and heat-treated graphene samples. XRD pattern of graphene shows a sharp and intensive peak centred at a diffraction angle (2θ) of 26·350. FTIR spectra of as-prepared and heated graphene were used to confirm the oxidation of graphite. TEM results indicated that the defect density and number of layers of graphene sheets were varied with heating temperature. The hexagonal sheet morphology and purity of as-prepared and heat treated samples were confirmed by SEM–EDX and Raman spectroscopy. The conductivity measurements revealed that the conductivity of graphene was decreased with an increase in heating temperature. The present study explains that graphene with enhanced functional properties can be achieved from the as-prepared sample.     

Enhancing the thermal conductivity of n-eicosane/silica phase change materials by reduced graphene oxide

Reduced graphene oxide (rGO) sheets prepared by different methods are incorporated to boost the thermal conductivity of organic phase change materials (n-eicosane) in silica microcapsules. Low concentration (1 wt%) of graphene dosing already results in notable increase of the thermal conductivity. The preparation methods of rGO significantly affect the thermal properties of the composite. With 1 wt% dosing, sodium borohydride (NaBH₄) reduced rGO increases the thermal conductivity by 83% and decrease the phase change enthalpy by 6%. On the other hand, the thermal reduced rGO increases the thermal conductivity by 193% but leads to a 15% loss of the phase enthalpy. The difference is attributed to the different surface morphology and functional groups of the rGO sheets.     

Conducting polymer coated graphene oxide reinforced C–epoxy composites for enhanced electrical conduction

Enhanced electrical conductivities were achieved in C–epoxy composites by integrating them with conducting polymers (CPs), namely poly pyrrole (PPY), poly(3,4-ethylene dioxythiophene) (PEDOT) and graphene oxide (GO) enwrapped by CPs. By in-situ polymerization of pyrrole or 3,4-ethylenedioxythiophene (EDOT) in the presence of the GO (template), sodium bis(2-ethylhexyl) sulfosuccinate (structure directing agent), ferric chloride (oxidant), the electrically conductive sheets of GO enwrapped CPs were obtained. The formation of CP coating on GO was confirmed by Raman spectroscopy, scanning electron microscopy and thermo gravimetric analysis studies. Different wt% of CP and CP coated GO were added to the epoxy resin and this resin was used to prepare the 2D laminated C–epoxy composites by hand layup method. DC electrical conductivity of the prepared C–epoxy composites were analyzed using current–voltage (I–V) characteristics and impedance measurements. Typical results showed that CP coated GO, at 0.5 wt% addition to epoxy imparted highest DC electrical conductivity for C–epoxy composite.     

锂离子电池硅/碳纳米管/石墨烯自支撑负极材料研究

通过真空驱动自组装法及蒸汽处理得到结构疏松的硅/碳纳米管/石墨烯自支撑负极材料(Si/CNTs/GP)。纳米硅颗粒(50 nm)为活性物质, 均匀分布在石墨烯片层结构中间; 石墨烯作为碳基体, 通过自组装构筑形成二维导电网络; 碳纳米管(CNTs)具有超高导电性和良好的力学强度, 它通过吸附作用均匀分布在石墨烯基体上形成导电的支撑网络结构。经过蒸汽处理后, 石墨烯层间距明显增大, 层与层之间不再是紧密堆叠的结构, 而是形成一种疏松、褶皱、内部空隙丰富的片层结构。Si/CNTs/GP负极材料中丰富的内部空穴和贯穿孔洞, 提供了材料很高的比表面积, 能有效提高电解液对材料的浸润性, 极大缩短了离子传输距离。同时这些内部空穴也有效缓冲硅充放电时的体积膨胀, 提高了材料的结构稳定性和电化学性能。该负极材料在4 A/g的大电流密度下容量维持在600 mAh/g, 表现出良好的大电流循环稳定性能。     

Electromechanical properties of nanotube-PVA composite actuator bimorphs

Oxidized multiwalled carbon nanotube (oxidized-MWNT)/polyvinyl alcohol (PVA) composite sheets have been prepared for electromechanical actuator applications. MWNT have been oxidized by nitric acid treatments. They were then dispersed in water and mixed with various amounts of PVA of high molecular weight (198?000?g?mol(-1)). The composite sheets were then obtained through a membrane filtration process. The composition of the systems has been optimized to combine suitable mechanical and electrical properties. Thermogravimetric analysis, mechanical tensile tests and conductivity measurements show that the best compromise of mechanical and electrical properties was obtained for a PVA weight fraction of about 30?wt%. In addition, one face of the sheets was coated with gold to increase the conductivity of the sheets and promote uniform actuation. Pseudo-bimorph devices have been realized by subsequently coating the composite sheets with an inert layer of PVA. The devices have been tested electromechanically in a liquid electrolyte (tetrabutylammonium/tetrafluoroborate (TBA/TFB) in acetonitrile) at constant frequency and different applied voltages, from 2 to 10?V. Measurements of the bimorph deflections were used to determine the stress generated by the nanotube-PVA sheets. The results show that the stress generated increases with increasing amplitude of the applied voltage and can reach 1.8?MPa. This value compares well with and even exceeds the stress generated by recently obtained bimorphs made of gold nanoparticles.     

Effects of functional groups on the graphene sheet for improving the thermomechanical properties of polyurethane nanocomposites

Dispersibility of graphene sheets in polymer matrices and interfacial interaction are challenging for producing graphene-based high performance polymer nanocomposites. In this study, three kinds nanofillers; pristine graphene nanoplatelets (GNPs), graphene oxide (GO), and functionalized graphene sheet (FGS) were used to prepare polyurethane (PU) composite by in-situ polymerization. To evaluate the efficacy of functional groups on the graphene sheets, PU reinforced with GNPs, GO, and FGS were compared through tensile testing and dynamic mechanical thermal analysis. The Young's moduli of 2 wt% GO and FGS based PU nanocomposites were found significantly higher than that of same amount of GNPs loading as an evidence of the effect of functional groups on graphene sheets for the mechanical reinforcement. The strong interaction of FGS with PU was responsible to exhibit notably high modulus (25.8 MPa) of 2 wt% FGS/PU composite than the same amount of GNPs and GO loading even at elevated temperature (100 °C).